Plasmas are widely used for a variety of treatment and layer deposition tasks in semiconductor fabrication and other thin film applications. These applications include subtractive processes such as wafer precleaning, contaminant removal, native oxide removal, photoresist removal, plasma etching, as well as treatment processes such as oxidation, nitridation, or hydridation of a layer both during and after formation. “Remote” plasma sources are frequently used, where the plasma is located at some distance from the surface to be treated or substrate on which a layer is being formed. The distance allows some filtering of the charged particles in the plasma. For example, the density of electrons and ions can be adjusted or removed from the generated plasma.
Logic devices are increasingly using germanium-based layers as the semiconductor channel in advanced transistors. The germanium-based layers may include germanium or silicon-germanium alloys. Germanium oxidizes more easily than silicon when exposed to ambient conditions. Further, the germanium oxides exhibit reduced stability when compared to the silicon oxides. Typically, these oxides must be removed before the formation of the transistor gate stack and/or the source and drain contacts to the transistor.
What is needed is a system and methods that enable the in-situ removal of native oxide such as the use of direct or remote plasmas to remove oxide layers present on semiconductor surfaces prior to further processing.